<ul id="tt" class="easyui-tree">
    <li>
        <span>Folder</span>
        <ul>
            <li>
                <span>Sub Folder 1</span>
                <ul>
                    <li><span><a href="#">File 11</a></span></li>
                    <li><span>File 12</span></li>
                    <li><span>File 13</span></li>
                </ul>
            </li>
            <li><span>File 2</span></li>
            <li><span>File 3</span></li>
        </ul>
    </li>
    <li><span>File21</span></li>
</ul>